This invention relates to deployable leads having electrodes which may be held in a position for inserting of the lead into the body of a patient, followed by placing of the electrodes into a position of use in which they assume a different configuration. More specifically, the invention relates to the field of implantable automatic defibrillators.
Examples of deployable defibrillation electrodes are disclosed in Fogarty et al. U.S. Pat. No. 4,860,769 and Moore U.S. Pat. No. 4,567,900 and Fain et al. co-pending U.S. Pat. application Ser. No. 404,517, filed Sep. 6, 1989.
As described in Fogarty et al. it is well known in the field of cardiology that certain types of cardiac arrhythmias known as ventricular tachycardia and fibrillation can often be effectively treated by the application of electrical shocks to the heart. Such defibrillation may be achieved by the application of electrical paddles to the chest of a patient, or directly to the heart tissue, if the chest is open during surgery.
More recent improvements have lead to the development of implantable defibrillators which monitor the heart for arrythmias and automatically initiate defibrillation when an arrythmia occurs. Such devices typically incorporate electrodes which are located next to the heart, or on an intravascular catheter, or both. Because the electrodes are closer to the heart tissue, implanted defibrillators require less electrical energy to stimulate the heart than do external electrodes.
However, major surgery is generally necessary to implant the present defibrillator lead systems, for example a median sternotomy or a lateral thoracotomy. These procedures can be very traumatic to the patient, and may have significant adverse side effects. Candidates for such procedures or any procedure include only those persons for whom the potential benefits outweigh the risks. Because of the significant surgical risks of the present lead systems, many patients who might otherwise benefit from the use of an implantable defibrillator are excluded.
While leads are generally known which are collapsed into an advancement position for implantation in the body and then are deployable to an operating position inside the body, the defibrillator lead electrodes require a substantially large area, to provide even current distribution and low defibrillation energy thresholds. Thus, difficulties are encountered in the designing of deployable defibrillator electrodes.
In electrodes such as those shown in Fogarty et al., it would be of advantage if the long, spiral electrode could be reduced in length. By this improvement, the length along which the electrode has to deploy is shorter and more controllable, and electrical resistance can be minimized. Similarly in the Moore patent, the size of the electrode, when distorted into shape for movement through a catheter as shown therein may be unduly large.
In accordance with this invention, a lead carrying multiple electrodes is provided to achieve a desired length reduction of the electrodes, as well as other significant advantages over electrodes of the prior art. For example, a multiple electrode system provides more redundance to the system so that it can continue to operate in the event of failure of one of the electrodes. Also, the lead of this invention may be inserted through a small incision with minimum trauma to the patient, while providing adequate electrode surface area for defibrillation, due to the deployable nature of the lead.